Native operating system services can prevent security software from installing arbitrary hooking within the kernel of operating systems. Security software is thus prevented from filtering all behaviors of an electronic device, including potentially malicious actions by malware. Malware may include, but is not limited to, spyware, rootkits, password stealers, sources of spam, sources of phishing attacks, sources of denial-of-service-attacks, viruses, loggers, Trojans, adware, or any other digital content that produces malicious activity.
An operating system's filtering functionality may be limited, and may only be available on timelines decided by the operating system vendor. Malware can operate and reside at the same level as security software, particularly in the operating system kernel and thus compromise both the operating system and the integrity of the security software itself.
Many forms of aggressive kernel mode malware tamper with user mode memory to accomplish malicious tasks such as injecting malicious code dynamically, modifying user mode code subsections to alter execution paths and redirect into malicious code, and modifying user mode data structures to defeat security software. Additionally, some malware may attack anti-malware applications and processes from the kernel by tampering with process memory code and data subsections to deceive the detection logic.
Kernel mode rootkits and other malware employ various methods to hide their presence from user mode applications and kernel mode device drivers. The techniques used may vary, depending upon where the infection takes place. For example, malware can attack the kernel active process list of an operating system to delist or unlink a rootkit or other malware process. Other malware may tamper with the code subsections of process access and enumeration functions.